Exterior Gateway Routing – 11 Points
4.1 BGP Peering
Easy task as there are not a lot of devices running BGP and all but one peering is on r6.
“All BGP traffic between r4 and r6 should traverse the VPN tunnel.”
Easy enough, just make the neighbor addresses 191.1.46.x. This also save me from configuring ‘ebgp multihop’ for the r4 <-> r6 peering.
4.2 BGP Bestpath Selection
Send all traffic for prefixes learned from AS 54 on r6 to BB1. Don’t use local_pref.
What about weight?
Best Path Selection Table:
|Attribute||Direction Applied||Traffic Flow Affected||Prefer|
Just set the weight from routes learned from BB1 to something greater than the default of 0 (IE used 100, I used 65000):
r6(config-router)#do sh ip bgp | i 220.127.116.11
*> 18.104.22.168 22.214.171.124 0 65000 54 50 60 i
*> 126.96.36.199 188.8.131.52 0 65000 54 50 60 i
*> 184.108.40.206 220.127.116.11 0 65000 54 i
*> 18.104.22.168 22.214.171.124 0 65000 54 i
*> 126.96.36.199 188.8.131.52 0 65000 54 i
*> 184.108.40.206 220.127.116.11 0 65000 54 i
*> 18.104.22.168 22.214.171.124 0 65000 54 i
*> 126.96.36.199 188.8.131.52 0 65000 54 i
4.3 BGP Filtering
Configure r6 so that AS 100 will not accept any prefixes from as 54 with a mask longer than /20. Use a single-line prefix-list.
The prefix-list bit is easy:
r6(config)#ip prefix-list LESSTHANTWENTY perm 0.0.0.0/0 le 20
There’s a really nice breakdown on prefix-lists in general in the IE solution guide.
I was thrown off by the SET_WEIGHT route-map in the IE solution guide, but it’s same route-map name they used in the previous task (I had named mine ‘WEIGHT’) with an additional line. So your final route-map should look similar to this:
route-map WEIGHT permit 10
match ip address prefix-list LESSTHANTWENTY
set weight 65000
4.4 BGP Summarization
Configure a summary of 184.108.40.206/16 and 220.127.116.11/20 but do not use aggregate-address. You are allowed to use two static routes on r3 to accomplish this.
I had NO CLUE on this one. I peeked the solution guide and then slapped my big, dumb forehead. The ip routes are to NULL0. You then redistribute the static routes. DOH!!!
r3(config)#ip route 18.104.22.168 255.255.240.0 null0
r3(config)#ip route 22.214.171.124 255.255.0.0 null0
r3(config)#router bgp 200
r6#sh ip route bgp | i 150|191.1.
126.96.36.199/16 is variably subnetted, 21 subnets, 4 masks
B 188.8.131.52/16 [20/0] via 184.108.40.206, 00:01:00
220.127.116.11/16 is variably subnetted, 10 subnets, 3 masks
B 18.104.22.168/20 [20/0] via 22.214.171.124, 00:01:00
4.5 BGP Table Stability
Configure r6 to not advertise 126.96.36.199/8 and 188.8.131.52/8 if they are “consistently unstable.”
The bgp dampening command is used to enable BGP route dampening. This command can be entered without any arguments or keywords. The half-life, reuse, suppress, and max-suppress-time arguments are position-dependent; meaning that if any of these arguments are entered, then all optional arguments must be entered.
When BGP dampening is configured and a prefix is withdrawn, BGP considers the withdrawn prefix as a flap and increases the penalty by a 1000. If BGP receives an attribute change, BGP increases the penalty by 500. If then the prefix has been withdrawn, BGP keeps the prefix in the BGP table as a history entry. If the prefix has not been withdrawn by the neighbor and BGP is not using this prefix, the prefix is marked as dampened. Dampened prefixes are not used in the BGP decision process and not installed to the routing table.
router bgp 100
bgp dampening route-map FLAPPERS
ip prefix-list FLAPPERS seq 5 permit 184.108.40.206/8
ip prefix-list FLAPPERS seq 10 permit 220.127.116.11/8
route-map FLAPPERS permit 10
match ip address prefix-list FLAPPERS
I missed on important piece though:
*Mar 6 18:15:27.386: %BGP-3-BADROUTEMAP: Bad parameters in the route-map FLAPPERS applied for Dampening
You MUST specify dampening parameters in the route map. Just use the defaults:
BGP dampening is disabled by default. The following values are used when this command is enabled without configuring any optional arguments:
half-life: 15 minutes
max-suppress-time: 4 times half-life
r6(config-router)#route-map FLAPPERS perm 10
r6(config-route-map)#set dampening 15 750 2000 60
r6#sh ip bgp dampening parameters
dampening 15 750 2000 60 (route-map FLAPPERS 10)
Half-life time : 15 mins Decay Time : 2320 secs
Max suppress penalty: 12000 Max suppress time: 60 mins
Suppress penalty : 2000 Reuse penalty : 750